Vibration isolators of the above-mentioned type are used in automobiles and other vehicles for engine mounting, cab mounting, body mounting, and so on. More particularly, the outer and inner cylinders are disposed in a parallel arrangement, and one of the two cylinders is connected with a member that vibrates and the other cylinder connects with another member to be isolated from vibration. The two liquid chambers are connected to each other by a flow restrictive passage, and at least one of the liquid chambers is partly defined by a flexible diaphragm. For example, JP-A No. 62-118133 shows a vibration isolator of this type. In such a vibration isolator, vibration is damped by elastic deformtion of the elastic body and movement of the liquid through the flow restrictive passage caused by deformation of the liquid chambers.
In Japanese Patent Application No. 62-152609 filed June 19, 1987 (not our published yet) and corresponding U.S. patent application Ser. No. 206,718 filed June 15, 1988, there is taught the provision of a hollow in the elastic body of a vibration isolator of the abovedescribed bushing type to prevent cracking or deterioration of the elastic body by the action of tensile force thereon. The hollow is located opposite to the liquid chambers with respect to the inner cylinder and extends over the entire length of the elastic body.
In a vibration isolator disclosed in the aforementioned patent applications, two liquid chambers are formed by scooping out the elastic body to provide a hollow opening in the cylindrical outer surface of the body and inserting a partition plate to divide the hollow into a radially inner chamber and a radially outer chamber. A hollow intermediate cylinder is fitted around the elastic body and is formed with an opening in a region facing the outer liquid chamber. A tubular elastic membrane is tightly inserted between the outer cylinder and the intermediate cylinder, and the tubular membrane is dented radially inward in a region where the intermediate cylinder is formed with the opening such that the dented part of the tubular membrane defines the radially outer periphery of the outer liquid chamber. The outer cylinder has a small hole in a section covering the opening in the intermediate cylinder so that the space between the outer cylinder and the dented part of the tubular elastic membrane becomes an air chamber communicating with the atmosphere. This vibration isolator is assembled in a liquid to be filled into the liquid chambers. Theelastic body formed in advance with the hollows bonded to the inner cylinder and the intermediate cylinder by vulcanization or curing.In the liquid, the tubular elastic membrane is fitted around the intermediate cylinder, and then the outer cylinder is fitted around and fixed by crimping to the intermediate cylinder. In the operations in the liquid it is not easy to accurately position the locally dented tubular membrane with respect to the opening in the wall of the intermediate cylinder, and, after that, it is difficult to completely extract the liquid from the aforementioned space to be made the air chamber by using the small hole in the outer cylinder.